a) Field of the Invention
This invention relates to a new or improved drum for use in a counterbalance system for overhead doors, and to a system and door installation employing such drum.
b) Description of the Prior Art
Over the years, numerous designs of counterbalance systems for upwardly opening or overhead doors have been devised, and examples are shown in various prior patents, such as U.S. 1,469,542 Storms, U.S. 1,603,379 Dautrick and U.S. 3,094,163 Herber, and more recently, an earlier design of my own shown in U.S. 4,887,658. The door opening arrangements disclosed in the foregoing patents make use of weights to provide the counterbalance force required during door opening. Door opening systems employing springs to provide the counterbalance force are well known, and are widely used, particularly in domestic garage doors.
Various forms of torsion or tension springs may be employed utilizing systems of cables and pulleys to transmit the spring force to the door. Spring operated counterbalance systems for doors tend to be troublesome to install, and while such systems are often not unduly expensive, they can be troublesome from the point of view of maintenance, and are subject to failure, for example through fracture of a spring or the like. Furthermore, with spring counterbalance systems it is difficult if not impossible to ensure that the spring force is accurately matched to the door load throughout the range of door opening movement.